The present invention relates to an electrical contact and, more particularly, to a contact which may be inserted into an aperture within an insulated mounting board assembly including a printed circuit board, for making electrical contact with conductive paths thereon without requiring solder. The contact is also utilized to make electrical contact with other conductive elements associated with the printed circuit board.
The modern mounting board assembly includes a number of small contact receiving holes on a mounting board located within a small area. Typically, these are plated holes. It is generally envisioned that a contact pin or the like will extend through each hole and make electrical connections with predetermined electrical components and/or the board itself. Because of the proximity of the board holes and therefore the contact pins, it is desirable to secure the pins to the mounting board without the use of external anchoring means. This has been most frequently accomplished with press-fit contact pins. Such pins have a press-fit section which is collapsibly inserted into the mounting board hole to exert a radial force on the portion of the board defining the hole. Frictional interaction between the press-fit section and the portion of the board defining the hole translates such radial force into a push-out force which retains the pin within the hole until a force exceeding such push-out force is applied to the pin. It is also highly desirable that a given press-fit pin, when used in holes within a wide range of sizes, be able to provide predetermined, substantially uniform, retention forces and positive internal contact over a large surface area without excessive damage to the hole or the conductive material which may line the hole.
Press-fit contact pins having solid, rectangular press-fit sections have been in common use for many years in the United States. The inherent problems of such pins have long been recognized, particularly that of the required close hole tolerances, the resultant excessive hole damage, the required high push-in forces, the necessity of a sophisticated pin replacement method, consisting of using replacement pins of larger cross section which, in turn, cause even more hole damage, and, the need for reflow soldering to assure the electrical connection needed for certain applications. However, simplicity and low initial cost have remained major considerations in pin choice and it is here that the press-fit contact pin having a solid, rectangular press-fit section enjoys its greatest advantage. Hence, with continued refinement, the performance of such pins has been deemed adequate and such pins have been accepted as the industry standard for some time.
In recent years, there has been a marked increase in the performance requirements for press-fit contact pins. With the advent of multi-layer, printed circuit board backplanes and with the stringent reliability requirement of the telecommunications and computer industries, which are rapidly adopting the printed circuit board backplane approach, has come the need for a press-fit contact pin of considerably improved operating capabilities. Such a pin should provide predetermined, substantially uniform, retention forces when used in holes within a wide range of sizes, i.e., when used in holes which are permitted large tolerances. The pin should distribute radial forces evenly enough within such holes to thereby provide positive, internal contact over a large surface area and minimize damage to the integrity of the hole and to conductive materials which may line the hole, provide sufficient push-out force to withstand the rigors of wire-wrapping and handling without requiring excessive push-in force, and obviate the need for specially sized replacement pins and reflow soldering.
Various contact pins, having press-fit sections departing from the traditional, solid, rectangular press-fit section, have been proposed. by way of example, two of such pins are discussed by P. J. Tamburro of Bell Laboratories, Whippany, N.J., in his paper, "RELIABILITY OF PRESS-FIT PINS IN PRINTED WIRING BOARDS". However, such pins have not been entirely effective in providing the aforesaid stated desired operating capabilities. Particularly, such pins are not able to operate in mounting board holes with large tolerances, e.g., in 0.040 inch "normal" holes with .+-.0.005 inch tolerance. Moreover, such pins have necessitated the sacrifice of the advantages of simplicity and low initial cost.
Key, in U.S. Pat. No. 4,017,143, discloses an improved compliant pin including a press-fit section comprising, in cross section, an open, curved arcuate segment, generally resembling a "C" shape. The dimensioning of the "C"-shaped press-fit section and the ductility-elasticity of the material from which it is formed are such that, when the pin is inserted into any one of a number of holes in a mounting board of a wide range of sizes, the "C"-shaped press-fit section undergoes plastic deformation in a substantial portion thereof.
"C"-shaped press-fit pins have not been completely satisfactory. Because the pin is asymmetrical in shape, the radial forces against its structure are not circumferentially uniform. Hence, there is no radial force at the mouth of the pin, and this is opposed by a substantial radial force at its backbone. The difficulty of this is that the pin, through repeated use, becomes deformed or structurally stressed and may even fail, causing problems with contact. It is desirous that a pin be provided that would have increased life over the "C"-shaped pins and which would advantageously provide firm, secure and assured contact with board holes for extended periods of time.